A variety of absorbent structures, for example, sanitary napkins, panty liners and the like, are constructed using pressure sensitive adhesives as positioning adhesives for attaching the article to the supporting garment.
There are a number of critical properties needed for these applications, specifically, the viscosity profile must be such that the adhesive will flow onto and partially penetrate the surface to which it is applied, yet allow a significant amount of the adhesive to remain on the exposed surface. Further, the adhesive coating must have good bond strength with high initial tack, yet the adhesive film must not transfer to the garment or cause pulling of the fibers or tearing of the garment when the absorbent article is removed.
Hot melt pressure sensitive adhesives are most commonly used for this positioning purpose with those disclosed in U.S. Pat. Nos. 4,136,699 and 4,704,110, being representative of the adhesives in current commercial use.
It has been proposed in U.S. Pat. No. 4,704,110 to utilize high styrene containing polymers, i.e., those containing greater than 35% styrene, in order to provide adhesives for positioning sanitary products to undergarments.
The commercial polymers referred to in the '110 patent generally had styrene contents in the range of 35 to 55 parts per 100 parts copolymer. Moreover, the block copolymers contained relatively low levels, i.e., less than about 15%, of divinyl functionality as a consequence of the actual polymerization reaction.
While the adhesives formulated therewith exhibited superior properties as contrasted with those available commercially at the time; there is a continuing need for adhesives exhibiting lower viscosity at temperatures of 130.degree. to 160.degree. C. which will enable the product to penetrate readily through the non-woven, thus allowing the positioning adhesive to also function as a construction adhesive.